Operating methods, data carriers, control devices, and X-ray apparatuses of said kind are generally known. They are used in particular for recording two-dimensional projections for a subsequent three-dimensional reconstruction of objects being examined.
The following procedure is broadly customary for recording the two-dimensional projections of the object being examined:
The object being examined or, as the case may be, the relevant area thereof is arranged in such a way that the relevant object area is locked in the crossover area of the swiveling axis and connecting line or, as the case may be, in the vicinity thereof. If, say, the object being examined is a person, then that person's heart or brain could be the relevant object area. In that case, for instance, a patient trolley on which the examinee is lying will be moved in such a way that the heart or, as the case may be, brain will be located in the above-cited crossover area.
A human heart, in particular, undergoes an iterative change—of course—because it has to beat, and so moves. It is, however, also possible for the relevant object area to change over time, independently of any movement. Consider, for example, how a contrast medium spreads in a vascular system or in an organ being supplied with blood (a muscle, including a heart muscle, the brain, the liver, . . . ). Particular consideration is given within the scope of the present invention to such cases in which the relevant object area changes over time.
The object being examined having been placed in position, the control device will drive the recording assembly in such a way that it will be swiveled around the swiveling axis. During said swiveling operation the control device drives the recording assembly in such a way that the X-ray detector will register two-dimensional projections of the object being examined in a multiplicity of angular positions, then convey them to the control device. The control device stores the projections conveyed to it, the corresponding angular positions, and status information about the object area changing over time.
In the older German patent application 10 2005 016 472.2 dated Apr. 8, 2005, not published by the submission date of the application for the present invention, a variant of the above-described method is described wherein not just a single swiveling operation is performed but a plurality thereof. Said older, not previously published application is not, though, a generally known state of the art but is to be considered only within the scope of the German patent-issuing process and, in the course thereof, only within the scope of the examination for novelty.
The two-dimensional projections of the object being examined that were registered for an X-ray apparatus applying the above-mentioned operating methods serve as the basis for a subsequent three-dimensional reconstruction, by means of a computer, of the object being examined.
It is furthermore described in the already mentioned German patent application 10 2005 016 472.2 dated Apr. 8, 2005, how, for each angular position for which the computer has determined a basic projection, to check whether an additional projection can also be determined, and, where applicable, to determine said additional projection also. It is crucial during said check for the status information of the additional projection also to correspond to the nominal status information.
If the computer determines an additional projection, it will determine a reconstruction projection for the respective angular position using the respective basic projection and respective additional projection. If it is unable to determine an additional projection, then the basic projection of the respective angular position will correspond to the reconstruction projection. The computer in each case ascertains the three-dimensional reconstruction using the reconstruction projections.
To be on the safe side, attention is at this point again drawn to the fact that the German patent application 10 2005 016 472.2 is not a generally known state of the art but is to be considered only within the scope of the German patent-issuing process and, in the course thereof, only within the scope of the examination for novelty.
It is furthermore described in the older German patent application 10 2004 061 933.6 dated Dec. 22, 2004, likewise not published by the submission date of the application for the present invention, that the two-dimensional projections are registered by means of two recording assemblies, with the X-ray detectors of the recording assemblies being of different size. In this case, for each angular position for which it has determined a basic projection the computer also determines an additional projection. The additional projection is independent of the status information. It is determined through having been registered by means of the larger of the two X-ray detectors. The computer determines in each case a reconstruction projection for the respective angular position using the basic projection and respectively corresponding additional projection. Using the reconstruction projections, the computer then ascertains the three-dimensional reconstruction of the object being examined. It applies also to the patent application 10 2004 061 933.6 that it is not a generally known state of the art but is to be considered only within the scope of the German patent-issuing process and, in the course thereof, only within the scope of the examination for novelty.
Two-dimensional projections of an object being examined for subsequently determining a three-dimensional reconstruction of said object are registered according to the prior art by means of, for example, angiography systems or what are termed C-arc systems, in particular mobile C-arc systems. The recording assembly is for that purpose swiveled through a swivel-angle range, which is to say between two final angular positions, around a swiveling axis. The swivel-angle range is as a rule greater than 180°, for example 200 to 225°. The three-dimensional reconstruction is determined according to, for instance, the Feldkamp algorithm generally known to persons skilled in the relevant art.
For certain applications it is necessary to perform a plurality of swiveling operations and to register two-dimensional projections during each of said operations. An instance of an application of said type is time-resolved heart imaging as described in, for example, the older German patent application 10 2005 016 472.2 dated Apr. 8, 2005. Perfusion measuring is another possible application.
The object being examined must of course also be X-rayed a corresponding number of times when projections are registered a number of times. The object being examined will consequently have a relatively high X-ray exposure.
To reduce the X-ray exposure it is already known how only to apply the full X-ray dosage when the object area changing over time (for example a person's heart) is momentarily in a phase condition requiring to be reconstructed. This procedure can, though, only be applied when it is known a priori in which phase condition the object area changing over time is to be reconstructed. This method for reducing the dosage cannot be applied if said phase condition is not known or if reconstructing is to be performed for a plurality of phase conditions.
To determine three-dimensional reconstructions it is necessary to use as large as possible an area of the X-ray detector and mask as little image information as possible through collimating of the X-ray beam. Artifacts will otherwise occur as a result of cut-off projections. Artifacts of said type are familiar to persons skilled in the relevant art as what are termed “truncation artifacts”. That is why all swiveling operations are performed in the prior art with a fully opened aperture device.